1. bookVolume 67 (2020): Issue 4 (December 2020)
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30 Mar 2016
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access type Open Access

Site characterization for engineering purposes using geophysical and geotechnical techniques

Published Online: 08 May 2021
Page range: 197 - 207
Received: 19 Feb 2021
Accepted: 08 Mar 2021
Journal Details
License
Format
Journal
First Published
30 Mar 2016
Publication timeframe
4 times per year
Languages
English
Abstract

Geophysical and geotechnical techniques were applied to determine the suitability of the sub-surface structure of Akole community area, Abeokuta, Nigeria, for the construction of engineering structures (CES). Four vertical electrical soundings (VES) were carried out, and 10 samples from different points at 1 m depth were analysed to determine soil moisture content, specific gravity (SG), Atterberg limits and California bearing ratio (CBR). The geoelectric sections revealed a maximum of five layers with the typical sounding curves of AKH and HKH types. Sieve analysis and tests for compaction limit, Atterberg limits, SG, optimum moisture content and maximum dry density for compaction limit revealed that samples SP2, SP3, SP4, SP6, SP7, SP8, SP9 and SP10 are of low plasticity with SG values that fall within the permissible range, while SP1 and SP5 are of medium plasticity and their SG values fall below the range of standard specifications. CBR analysis showed that SP1 and SP5 have low load-bearing capacities. VES 1 and 2, linked with SP1 and SP5, are considered unstable and unsuitable to support the CES with shallow foundations; however, excavation of weak layers up to a depth of 5 m and reinforcement will enable the support.

Keywords

Ključne besede

Introduction

Developing nations have suffered from recurring collapse of engineering structures over the years due to failure to carry out necessary investigations before the structures are erected [1,2,3]. Recently, the statistics of failures of building and engineering structures throughout the nation has increased geometrically [4]. Factors responsible for failure of engineering structures are often attributed to substandard usage of building materials, old age of buildings, improper foundation design, non-compliance to specifications, inadequate supervision and nature of the sub-surface conditions of the ground on which the building is sited [5, 6]. The aftermath of structural failure of buildings is always huge, including loss of lives and valuable properties, as well as loss of financial investment.

Since the earth provides support for every engineering structure, it is important to conduct preconstruction investigation of the sub-surface of any proposed site. This is to ascertain the strength and the competence of the subsoil earth materials, as well as to carry out the timed post-construction monitoring of such structure to ensure its integrity [4, 7,]. Geophysical methods (particularly, the electrical resistivity technique) have been widely used for an extensive variety of engineering and environmental problems because of their reliability, efficiency and cost-effectiveness [4, 8]. The electrical resistivity technique has also proved to be a reliable tool for obtaining detailed information about the sub-surface structure, particularly for detecting irregularities in and the complexity of the geological sub-surface [9].

Geotechnical study is another investigative approach that can provide excellent insight into the engineering properties of sub-surface soil materials [5]. The geotechnical test uses the principle of soil and rock mechanics to investigate the sub-surface condition and to determine the relevant physical properties of the materials. Information, such as soil type, load-bearing capacity of materials, zone of weakness, resistance to penetration, compressibility and shrinkage limit, among others, is often necessary before designing a very good and strong foundation for a proposed engineering structure [10].

Site characterization for building construction purposes at the Federal University of Agriculture, Abeokuta, Nigeria, was conducted using geophysical and geotechnical methods [11]. The area considered in the study was found to be suitable for both shallow and deep foundations. However, there were some exceptions at a few points, wherein reinforcement was required to support shallow and deep foundations. Subsoil evaluation of the pre-foundation at the proposed site at the Polytechnic of Ibadan was conducted [12] using geophysical and geotechnical techniques. The study revealed that the clay content of the soil is low; the subsoil of the study area was therefore rated to be competent as foundation material to support the proposed structure.

Adequate understanding of soil properties is of paramount importance in the study of foundation integrity because it provides information on the material properties of the soils, including ability to support the load often exerted by the structure erected. The objective of this study is to use geophysical and geotechnical techniques to investigate the nature and engineering properties of the sub-surface, its strength and capability (or otherwise) to bear the load of the engineering structure to be erected in Akole Community, Oke-Ata, Abeokuta, Southwestern Nigeria.

Materials and methods
Geomorphology and geology of the study area

The study area is located at Akole Community in Oke-Ata, Abeokuta North, Ogun State, Southwestern Nigeria, which lies between latitudes 7°8′16.9″ N and 7°8′24″ N and longitudes 3°17′9.2″ E and 3°17′13.4″ E. The ground in the study area lies at an elevation between 62 m and 78 m above sea level (Figure 1).

Figure 1

Topographical map of the study area showing profile base image.

The climate is warm and tropical due to the rain-bearing ocean wind of the south-western monsoon and the northwest wind that arises from the Sahara desert. The rainy season of the study area starts around April and ends in October, with rainfall of nearly 1,238 mm per annum, while the dry season starts in November and ends in March. The area is located in a hummocky terrain with a well-pronounced undulating topography and prominent hills, characterized by a moderate slope varying in altitude. The study area falls within the Precambrian Basement rocks of Southwestern Nigeria, with six major lithologic units, namely quartzite, banded-gneiss, biotite-schist, quartz-biotite schist and pegmatite [13].

Fieldwork procedure for geophysical survey

The method used for the geophysical survey was the vertical electrical sounding (VES) using the Schlumberger electrode array. The Schlumberger array focusses on the vertical variation of sub-surface layers. The Schlumberger configuration of an electrode is quite sensitive to vertical sub-surface resistivity below the centre of the array and it is less sensitive to horizontal changes in the sub-surface [14]. Data from a total of four VESs were acquired in the study area, and each of the potential differences and currents measured at each point were recorded. The apparent resistivity (ρa) was computed from measurements of voltage (ΔV) and current (i) using Equation 1. ρa=π[(s2-a2)/4]aΔVi {\rho _a} = {{\pi \left[ {\left({{s^2} - {a^2}} \right)/4} \right]} \over a}{{\Delta V} \over i} where ρa is the apparent resistivity obtained, s is the distance between the potential electrodes, a is the distance between the current electrodes, ΔV is the potential difference measured and i is the current measured.

Using WinResist software, the apparent resistivity values obtained were plotted against the electrode spacing to acquire the VES curves.

Geotechnical method (laboratory tests for geotechnical survey)

The soil moisture content (SMC), which is the water between the pores of the soil, was determined using the gravimetric method expressed by Equation 2 [15].

SMC=((massofContainer+moistsoil)-(massofContainer+drysoil)(massofContainer+drysiol)-(massofContainer)) {\rm{SMC}} = \left({{{(mass\,of\,Container + moistsoil) - (mass\,of\,Container + drysoil)} \over {(mass\,of\,Container + drysiol) - (mass\,of\,Container)}}} \right)

The Atterberg limit test verifies the liquid (LL) and plastic (PL) limits of a fine-grained soil. The LL refers to the moisture content at which the soil begins to behave as a liquid material and begins to flow, while the PL is defined as the moisture content at which soil begins to behave as a plastic material. The LL and PL were determined using the Casagrande method, as described in American Society for Testing and Materials (ASTM) Standard D4318. The difference between the LL and the PL gives the plasticity index (PI). The compaction limit test describes the relationship between the moisture content and the dry density of a soil for a specified compactive effort (amount of energy that is applied to the soil). The compaction properties were determined using standard methods (ASTM D698 and ASTM D1557), the standard and modified efforts of 6,000 kN-m/m3 and 27,000 kN-m/m3, respectively, were chosen for the determination of the moisture–density relationship. The California bearing ratio (CBR) expresses the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min to that required for the corresponding penetration of a standard material [16]. The CBR was determined following the procedure of ASTM D1883.

The specific gravity (SG) of the soil was determined using a water pycnometer-based standard test (ASTM D854-00) expressed by Equation 3. SG=((w2-w1)(w2-w1)-(w-w4)), SG = \left({{{({w_2} - {w_1})} \over {({w_2} - {w_1}) - (w - {w_4})}}} \right), where w1 = empty weight of pycnometer, w2 = weight of pycnometer + oven-dried soil, w3 = weight of pycnometer + oven-dried soil + water, and w4 = weight of pycnometer + water.

The grain size analysis estimates the percentage of sand that was passed or retained by an individual sieve. A soil sample of 500 g was sieved to appropriate sieve sizes of 475, 236, 118, 600, 300, 150, 75 μm and weighed. The percentages of particles passing and particles retained, as well as the quantity passing, were calculated using Equations 4, 5 and 6, respectively. P=MrTm*100, P = {{Mr} \over {Tm}}*100, R=100-P, R = 100 - P, QP=Tm-Mr, {Q_P} = {T_m} - {M_r}, where Tm = total mass of the soils, R = percentage retained, P = percentage passing, Mr = mass retained and QP = quantity passing.

Data processing and interpretation
Characteristics of the VES layers
VES 1

The geoelectric curve for VES 1 (Figure 2) depicts five different sub-surface layers, which are as follows: topsoil, with resistivity value of 180 Ω·m, thickness of 0.913 m and depth of 0.913 m; sandy clay, with resistivity value of 145 Ω·m, thickness of 1.24 m and depth of 2.15 m; laterite, with resistivity value of 332 Ω·m, thickness of 1.56 m and depth of 3.71 m; saturated sandy clay, with resistivity value of 107 Ω·m, thickness of 4.47 m and depth of 8.18 m; weathered basement, with resistivity value of 3,385 Ω·m and an inestimable thickness. Due to shrinkage and swelling of clayey soils, excavation must be done until an adequate-load-bearing layer is reached for shallow foundation construction within the VES Profile 1 region.

Figure 2

Graph of apparent resistivity against electrode spacing for VES Profile 1. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

VES 2

The geoelectric curve for VES 2 (Figure 3) depicts four different sub-surface layers, which include the following: topsoil, with resistivity value of 248 Ω·m, thickness of 0.867 m and depth of 0.867 m; sandy clay, with resistivity value of 190 Ω·m, thickness of 4.03 m and depth of 4.9 m; saturated sandy clay, with resistivity value of 175 Ω·m, thickness of 11.9 m and depth of 16.8 m; weathered basement, with resistivity value of 240 Ω·m and an immeasurable thickness. The compactness of the soil increases as the depth below the earth’s sub-surface increases; hence, it is strongly advised to increase the depth of the foundations constructed in VES Profile 2 to a depth not less than 3.1 m.

Figure 3

Graph of apparent resistivity against electrode spacing for VES Profile 2. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

VES 3

Four different sub-surface layers were delineated for VES 3: the topsoil, with resistivity value of 267 Ω·m, thickness of 0.573 m and depth of 0.573 m; sandy clay, with resistivity value of 167 Ω·m, thickness of 0.833 m and depth of 1.41 m; indurated sandy clay, with resistivity value of 671 Ω·m, thickness of 9.92 m and depth of 11.3 m; weathered basement, with resistivity value of 4,041 Ω·m and an inestimable thickness (Figure 4). The soil constituents in the topsoil are fairly suitable for use in shallow foundations, while further reinforcement is essential for deep foundations.

Figure 4

Graph of apparent resistivity against electrode spacing for VES Profile 3. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

VES 4

Four major sub-surface geoelectric layers were delineated from the interpretation results of VES 4; these include the following: the topsoil, with resistivity value of 290 Ω·m, thickness of 0.564 m and depth of 0.564 m; sandy clay, with resistivity value of 167 Ω·m, thickness of 0.752 m and depth of 1.32 m; indurated sandy clay, with resistivity value of 623 Ω·m, thickness of 7.81 m and depth of 9.13 m; weathered basement, with resistivity value of 4,355 Ω·m and an infinite thickness (Figure 5). The particles of soil constituting the topsoil are suitable for use in shallow foundations, and additional strengthening is necessary for deep foundations.

Figure 5

Graph of apparent resistivity against electrode spacing for VES Profile 4. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

The VES profiles delineated a maximum of five geoelectric sub-surface layers. These are the top soil, sandy clay, laterite, saturated and indurated sandy clay, and basement rock with shallow sub-surface. The top soil – with resistivity values varying from 180 Ω·m to 290 Ω·m and thickness ranging from 0.56 m to 0.91 m – is composed of clayey sand and sand. The top-soil particles are relatively suitable for use in shallow foundations. The second layer is composed of sandy clay and clayey sand, with resistivity values ranging from 107 Ω·m to 332 Ω·m and thickness values between 0.76 m and 11.9 m. Saturated and indurated sandy clays have resistivity values varying from 240 Ω·m to 671 Ω·m and thickness varying between 7.81 m and 9.92 m, and the weathered/fresh basement has resistivity values ranging from 240 Ω·m to 4,355 Ω·m, with the depth to bedrock generally being <20 m. The best layer that acts as hard rock terrain is the A-type. The A-combination types are characterized by high load-bearing capacity [17]. In the study area, A-combination types (AKH-3 and HKH-1) constitute 75% (Table 1) of the VES survey points, which suggest capacity for load bearing.

Summary of the results of the VESs for the study area

VES Location No. of layers Resistivity (Ωm) Thickness (m) Depth (m) Inferred lithology Curve type
1 Latitude 7°08′ 17.2″ 1 180 0.91 0.91 Topsoil AKH
Longitude 3° 17′ 13.2″ 2 145 1.24 2.15 Sandy clay
3 332 1.56 3.71 Laterite
4 107 4.47 8.18 Saturated sandy clay
5 3,385 Fresh basement

2 Latitude 7° 08′ 17.0″ 1 248 0.86 0.86 Topsoil HKH
Longitude 3° 17′ 12.9″ 2 190 4.03 4.90 Clayey sand
3 175 11.9 16.8 Saturated sandy clay
4 240 Weathered basement

3 Latitude 7° 08′ 17.2″ 1 267 0.57 0.57 Topsoil AKH
Longitude 3° 17′ 10.0″ 2 167 0.83 1.41 Sandy clay
3 671 9.92 11.3 Indurated sandy clay
4 4,041 Fresh basement

4 Latitude 7° 08′24.0″ 1 290 0.56 0.56 Topsoil AKH
Longitude 3° 17′ 10.3″ 2 167 0.75 1.32 Sandy clay
3 623 7.81 9.13 Indurated sandy clay
4 4,355 Fresh basement

The geoelectric sections and representative horizontal electrical profiling curves of the study area revealed that the lithology of the area is made up of topsoil, sandy clay, laterite (covering a few portions), saturated/Indurated sandy clay and weathered/fresh basement rock (Figure 6).

Figure 6

Profiles of the geoelectric sections of the VES stations.

Geotechnical results and discussion
Interpretation of Atterberg limit test

The PI of the soil samples (Table 2) revealed that soil samples SP2, SP3, SP4, SP6, SP7, SP8, SP9 and SP10 fall between PIs of 1% and 10%, which implies low plasticity, consisting of sand or silt with traces of clay, while soil samples SP1 and SP5 have PIs between 10% and 20%, depicting medium plasticity and composed of clayey loam soil. All the soil samples SP1–SP10 fall within the limits of the specifications, except SP1 and SP5, for which the LL and the PI exceeded the stipulated values of 35% and 12%, respectively, contrary to the Federal Ministry of Works and Housing (FMW&H) specification requirement in Clauses 6201 and 6252. The PI of soil samples SP1 and SP5 is above the standard limit and, therefore, they are considered to be highly plastic, which may pose a threat to the structure and consequently lead to structural failure.

Results of analyses of the Atterberg limits, SG, moisture content and compaction limit

Sample points SP1 SP2 SP3 SP4 SP5 SP6 SP7 SP8 SP9 SP10
LL 38.50 28.00 18.75 17.65 37.56 25.85 18.67 17.34 15.28 14.39
PL 23.97 18.25 13.5 14.09 24.21 17.96 13.81 12.37 12.63 11.98
PI 14.53 9.75 5.25 3.56 13.35 7.89 4.86 4.97 2.65 2.41
1st SG 2.35 2.55 2.64 2.38 2.40 2.67 2.58 2.71 2.57 2.75
2nd SG 2.45 2.57 2.80 2.80 2.45 2.67 2.55 2.38 2.71 2.50
Average SG 2.40 2.56 2.72 2.59 2.43 2.67 2.57 2.69 2.64 2.63
OMC (%) 38.67 14.90 15.20 16.52 47.56 13.94 16.24 11.87 12.57 10.21
MDD (kg/m3) 1,445 2,506 2,100 1,720 1,250 2,850 1,790 3,011 2,910 3,500
Moisture content 23.97 17.25 13.50 14.09 24.21 16.03 13.81 12.34 12.63 11.98

LL, liquid limit; PL, plastic limit; PI, plasticity index; SG, specific gravity; OMC, optimum moisture content; MDD, maximum dry density; SP, sampling point.

Results of the SG test

Table 2 shows the SG values obtained for the different soil samples. All the samples fall between the ranges of specification, varying from 2.5 to 2.75, excluding samples SP1 and SP5, which fall below the limit recommended by FMW&H [18]. In a previous paper [19], it was noted that the SG of soil grains is a key attribute in the assessment of aggregate parameters for construction purposes. The higher the SG of the soil towards the upper limit of the soil standard, the better is the soil for construction purposes.

Soil moisture content

All the samples (Table 2) have moderate moisture content, except for samples SP1 and SP5, which have very high moisture content. Samples SP1 and SP5 are considered to be poor for engineering purpose because of their high content of moisture, and this implies that they have high ability to retain water without releasingit.

Results of the compaction limit test

The results for the compaction limit test for each sample shown in Table 2 illustrates that the MDD for the soil samples ranges from 1,250 kg/m3 to 3,500 kg/m3, and the OMC ranges from 10.21% to 47.56%. All the samples, except SP1 and SP5, fall within the specifications of the FMW&H (1997), which recommends the MDD to be >1,680 kg/m3 and the OMC to be <18%. The density of the soil mass affects the strength of the soil, which implies that SP1 and SP5 have lower values compared to the standard values. The strength of a soil increases as its dry density increases; the potential for the soil to take on water at later times is decreased by higher densities.

Results of the CBR test

The overall CBR values for the soaked (CBR_s) and unsoaked (CBR_u) samples, as shown in Table 3, fall within the specified limits for all the soil samples analysed, except for SP1 and SP5. The FMW&H specification states that the minimum strength of the material should not be <80% for CBR (for unsoaked samples), while the minimum strength of the material should not be <10% after at least 48 h of soaking (for soaked samples). The CBR_s values ranged from 3.05% to 29.76%, while CBR_u ranged from 60.25% to 98.95%. The values for CBR_u and CBR_s are 60.25% and 5.62% for SP1 and 70.45% and 3.95% for SP5, respectively. This implies that the soil is clayey lateritic type of soil, which does not support heavy structures. In addition, moisture influx would be highly detrimental to the structures constructed at those locations.

Results of the CBR test for the soil samples

Sampling point Location CBR_u (%) CBR_s (%)
SP1 Latitude 7° 08′ 15.8″Longitude 3° 17′ 13.3″ 60.25 5.62
SP2 Latitude 7° 08′ 17.2″Longitude 3° 17′ 13.2″ 89.34 14.00
SP3 Latitude 7° 08′ 18.8″Longitude 3° 17′ 13.3″ 91.00 18.00
SP4 Latitude 7° 08′ 20.5″Longitude 3° 17′ 13.4″ 97.00 21.00
SP5 Latitude 7° 08′ 17.0″Longitude 3° 17′ 13.0″ 70.45 3.95
SP6 Latitude 7° 08′ 16.9″Longitude 3° 17′ 11.3″ 84.37 12.89
SP7 Latitude 7° 08′ 17.2″Longitude 3° 17′ 10.0″ 90.56 20.86
SP8 Latitude 7° 08′ 18.8″Longitude 3° 17′ 10.0″ 97.96 27.95
SP9 Latitude 7° 08′ 20.5″Longitude 3° 17′ 10.0″ 98.95 29.76
SP10 Latitude 7° 08′ 24.0″Longitude 3° 17′ 10.3″ 98.00 28.00

Notes: CBR, California bearing ratio; CBR_s, CBR of soaked sample; CBR_u, CBR of unsoaked sample; SP, sampling point.

Results of sieve analysis

All the soil samples SP1–SP10 (Table 4) fall within the limit of specifications for sieve analysis since the percentage by weight of 15.18% passing the No. 200 sieve does not exceed the stipulated value of 35%, as required by the FMWH (1997) in Clause 6201.

Summary of the results of sieve analysis

Sample Sieve number Diameter (μm) 4475 8236 16118 30600 50300 100150 20075 PAN
SP1 % Retained 14.43 12.70 12.99 13.99 9.05 13.08 11.26 12.50
% Passing 85.57 72.87 59.88 45.89 36.84 23.76 12.50 0
SP2 % Retained 9.35 9.83 12.49 12.88 13.5 14.56 15.51 11.88
% Passing 90.65 80.82 68.33 55.45 41.95 27.39 11.88 0
SP3 % Retained 9.72 10.06 12.27 12.43 12.79 14.62 15.60 12.51
% Passing 90.28 80.22 67.95 55.52 42.73 28.11 12.51 0
SP4 % Retained 9.73 13.37 12.39 12.48 13.67 12.81 13.05 12.5
% Passing 90.27 76.9 64.51 52.03 38.36 25.55 12.50 0
SP5 % Retained 10.04 10.23 12.35 12.53 12.67 14.63 15.04 12.51
% Passing 89.96 79.73 67.38 54.85 42.18 27.55 12.51 0
SP6 % Retained 9.91 10.29 12.01 12.51 12.98 14.6 15.19 12.51
% Passing 90.09 79.80 67.79 55.28 42.3 27.7 12.51 0
SP7 % Retained 9.93 10.43 12.56 12.7 13.32 15.56 13.00 12.50
% Passing 90.07 79.64 67.08 54.38 41.06 25.5 12.5 0
SP8 % Retained 10.21 10.31 12.03 12.54 13;00 14.63 14.96 12.32
% Passing 89.79 79.48 67.45 54.91 41.91 27.28 12.32 0
SP9 % Retained 9.84 10.37 12.41 12.24 13.02 14.56 15.03 12.53
% Passing 90.16 79.79 67.38 55.14 42.12 27.56 12.53 0
SP10 % Retained 9.95 10.25 12.25 12.47 12.90 14.50 15.18 12.50
% Passing 90.05 79.80 67.55 55.08 42.18 27.68 12.50 0

Note: SP, sampling point.

Conclusion

A series of geophysical and geotechnical investigations have been carried out to give proper insight into the nature of sub-surface dispositions and their delineation to ensure building foundation integrity in the study area. The inferred lithology from the VES results revealed a maximum of five geoelectric layers. The geotechnical method, which involved Atterberg limit tests, shows that all the soil samples have low PI and are composed of sand or silt with traces of clay, except samples SP1 and SP5 (soil samples extracted from VES 1 and VES 2), which have medium PI and are composed of clay soil. Soil samples SP1 and SP5 exceeded the stipulated value limit and therefore pose a threat of structural failure. All the soil samples, except SP1 and SP5, had average SG values within the range of standard specifications. The laboratory result for the CBR for soil samples SP1 and SP5 indicated that the soil is clayey lateritic, which is highly detrimental to structures due to influx of moisture. The sieve analysis result showed that the entire set of soil samples has a size range within the limit of specifications and does not exceed the standard value. The result for compaction limit revealed that all the soil samples are within the specified standard, except SP1 and SP5. It is vital to note that shallow foundations for any engineering structure are considered unsuitable at the weak zones because of the presence of incompetent materials, which tend to pose a threat to the development of future civil engineering structures in any given area.

Figure 1

Topographical map of the study area showing profile base image.
Topographical map of the study area showing profile base image.

Figure 2

Graph of apparent resistivity against electrode spacing for VES Profile 1. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.
Graph of apparent resistivity against electrode spacing for VES Profile 1. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

Figure 3

Graph of apparent resistivity against electrode spacing for VES Profile 2. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.
Graph of apparent resistivity against electrode spacing for VES Profile 2. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

Figure 4

Graph of apparent resistivity against electrode spacing for VES Profile 3. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.
Graph of apparent resistivity against electrode spacing for VES Profile 3. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

Figure 5

Graph of apparent resistivity against electrode spacing for VES Profile 4. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.
Graph of apparent resistivity against electrode spacing for VES Profile 4. Notes: Blue line represents the phase values on the cross sections; the red line represents true resistivity; the black line in the graph represents apparent resistivity.

Figure 6

Profiles of the geoelectric sections of the VES stations.
Profiles of the geoelectric sections of the VES stations.

Summary of the results of the VESs for the study area

VES Location No. of layers Resistivity (Ωm) Thickness (m) Depth (m) Inferred lithology Curve type
1 Latitude 7°08′ 17.2″ 1 180 0.91 0.91 Topsoil AKH
Longitude 3° 17′ 13.2″ 2 145 1.24 2.15 Sandy clay
3 332 1.56 3.71 Laterite
4 107 4.47 8.18 Saturated sandy clay
5 3,385 Fresh basement

2 Latitude 7° 08′ 17.0″ 1 248 0.86 0.86 Topsoil HKH
Longitude 3° 17′ 12.9″ 2 190 4.03 4.90 Clayey sand
3 175 11.9 16.8 Saturated sandy clay
4 240 Weathered basement

3 Latitude 7° 08′ 17.2″ 1 267 0.57 0.57 Topsoil AKH
Longitude 3° 17′ 10.0″ 2 167 0.83 1.41 Sandy clay
3 671 9.92 11.3 Indurated sandy clay
4 4,041 Fresh basement

4 Latitude 7° 08′24.0″ 1 290 0.56 0.56 Topsoil AKH
Longitude 3° 17′ 10.3″ 2 167 0.75 1.32 Sandy clay
3 623 7.81 9.13 Indurated sandy clay
4 4,355 Fresh basement

Results of analyses of the Atterberg limits, SG, moisture content and compaction limit

Sample points SP1 SP2 SP3 SP4 SP5 SP6 SP7 SP8 SP9 SP10
LL 38.50 28.00 18.75 17.65 37.56 25.85 18.67 17.34 15.28 14.39
PL 23.97 18.25 13.5 14.09 24.21 17.96 13.81 12.37 12.63 11.98
PI 14.53 9.75 5.25 3.56 13.35 7.89 4.86 4.97 2.65 2.41
1st SG 2.35 2.55 2.64 2.38 2.40 2.67 2.58 2.71 2.57 2.75
2nd SG 2.45 2.57 2.80 2.80 2.45 2.67 2.55 2.38 2.71 2.50
Average SG 2.40 2.56 2.72 2.59 2.43 2.67 2.57 2.69 2.64 2.63
OMC (%) 38.67 14.90 15.20 16.52 47.56 13.94 16.24 11.87 12.57 10.21
MDD (kg/m3) 1,445 2,506 2,100 1,720 1,250 2,850 1,790 3,011 2,910 3,500
Moisture content 23.97 17.25 13.50 14.09 24.21 16.03 13.81 12.34 12.63 11.98

Summary of the results of sieve analysis

Sample Sieve number Diameter (μm) 4475 8236 16118 30600 50300 100150 20075 PAN
SP1 % Retained 14.43 12.70 12.99 13.99 9.05 13.08 11.26 12.50
% Passing 85.57 72.87 59.88 45.89 36.84 23.76 12.50 0
SP2 % Retained 9.35 9.83 12.49 12.88 13.5 14.56 15.51 11.88
% Passing 90.65 80.82 68.33 55.45 41.95 27.39 11.88 0
SP3 % Retained 9.72 10.06 12.27 12.43 12.79 14.62 15.60 12.51
% Passing 90.28 80.22 67.95 55.52 42.73 28.11 12.51 0
SP4 % Retained 9.73 13.37 12.39 12.48 13.67 12.81 13.05 12.5
% Passing 90.27 76.9 64.51 52.03 38.36 25.55 12.50 0
SP5 % Retained 10.04 10.23 12.35 12.53 12.67 14.63 15.04 12.51
% Passing 89.96 79.73 67.38 54.85 42.18 27.55 12.51 0
SP6 % Retained 9.91 10.29 12.01 12.51 12.98 14.6 15.19 12.51
% Passing 90.09 79.80 67.79 55.28 42.3 27.7 12.51 0
SP7 % Retained 9.93 10.43 12.56 12.7 13.32 15.56 13.00 12.50
% Passing 90.07 79.64 67.08 54.38 41.06 25.5 12.5 0
SP8 % Retained 10.21 10.31 12.03 12.54 13;00 14.63 14.96 12.32
% Passing 89.79 79.48 67.45 54.91 41.91 27.28 12.32 0
SP9 % Retained 9.84 10.37 12.41 12.24 13.02 14.56 15.03 12.53
% Passing 90.16 79.79 67.38 55.14 42.12 27.56 12.53 0
SP10 % Retained 9.95 10.25 12.25 12.47 12.90 14.50 15.18 12.50
% Passing 90.05 79.80 67.55 55.08 42.18 27.68 12.50 0

Results of the CBR test for the soil samples

Sampling point Location CBR_u (%) CBR_s (%)
SP1 Latitude 7° 08′ 15.8″Longitude 3° 17′ 13.3″ 60.25 5.62
SP2 Latitude 7° 08′ 17.2″Longitude 3° 17′ 13.2″ 89.34 14.00
SP3 Latitude 7° 08′ 18.8″Longitude 3° 17′ 13.3″ 91.00 18.00
SP4 Latitude 7° 08′ 20.5″Longitude 3° 17′ 13.4″ 97.00 21.00
SP5 Latitude 7° 08′ 17.0″Longitude 3° 17′ 13.0″ 70.45 3.95
SP6 Latitude 7° 08′ 16.9″Longitude 3° 17′ 11.3″ 84.37 12.89
SP7 Latitude 7° 08′ 17.2″Longitude 3° 17′ 10.0″ 90.56 20.86
SP8 Latitude 7° 08′ 18.8″Longitude 3° 17′ 10.0″ 97.96 27.95
SP9 Latitude 7° 08′ 20.5″Longitude 3° 17′ 10.0″ 98.95 29.76
SP10 Latitude 7° 08′ 24.0″Longitude 3° 17′ 10.3″ 98.00 28.00

Amadi, A.N., Eze, C.J., Igwe, C.O., Okunlola, I.A., Okoye, N.O. (2012): Architects and geologists view on the causes of building failures in Nigeria. Modern Applied Science, 6(6), pp. 31, DOI:10.5539/mas.v6n6p31. AmadiA.N. EzeC.J. IgweC.O. OkunlolaI.A. OkoyeN.O. 2012 Architects and geologists view on the causes of building failures in Nigeria Modern Applied Science 6 6 31 10.5539/mas.v6n6p31 Open DOISearch in Google Scholar

Ayininuola, G.M., Olalusi, O.O. (2004): Assessment of building failures in Nigeria: Lagos and Ibadan Case Study. African Journal of Science and Technology, 5(1), pp. 73–78, DOI:10.4314/ajst.v5i1.15321. AyininuolaG.M. OlalusiO.O. 2004 Assessment of building failures in Nigeria: Lagos and Ibadan Case Study African Journal of Science and Technology 5 1 73 78 10.4314/ajst.v5i1.15321 Open DOISearch in Google Scholar

Dimuna, K.O. (2010): Incessant incidents of building collapse in Nigeria. A challenge to stakeholders. Global Journal of Researches in Engineering, 10(4), pp. 75–84. DimunaK.O. 2010 Incessant incidents of building collapse in Nigeria. A challenge to stakeholders Global Journal of Researches in Engineering 10 4 75 84 Search in Google Scholar

Oyedele, K.F., Okoh, C. (2011): Subsoil investigation using integrated methods at Lagos, Nigeria. Journal of Geology and Mining Research, 3(7), pp. 169–179. OyedeleK.F. OkohC. 2011 Subsoil investigation using integrated methods at Lagos, Nigeria Journal of Geology and Mining Research 3 7 169 179 Search in Google Scholar

Olayanju, G.M., Mogaji, K.A., Lim, H.S., Ojo, T.S. (2017): Foundation integrity assessment using integrated geophysical and geotechnical techniques: Case study in crystalline basement complex, Southwestern Nigeria. Journal of Geophysics and Engineering, 14(3), pp. 675–690, DOI:10.1088/1742-2140/aa64f7. OlayanjuG.M. MogajiK.A. LimH.S. OjoT.S. 2017 Foundation integrity assessment using integrated geophysical and geotechnical techniques: Case study in crystalline basement complex, Southwestern Nigeria Journal of Geophysics and Engineering 14 3 675 690 10.1088/1742-2140/aa64f7 Open DOISearch in Google Scholar

Oluwafemi, O., Ogunribido, T.H. (2014): Integrated geophysical and geotechnical assessment of the permanent site of Adekunle Ajasin University, Akungba-Akoko, Southwestern, Nigeria. Pelagia research library, 5(2), pp. 199–209. OluwafemiO. OgunribidoT.H. 2014 Integrated geophysical and geotechnical assessment of the permanent site of Adekunle Ajasin University, Akungba-Akoko, Southwestern, Nigeria Pelagia research library 5 2 199 209 Search in Google Scholar

Oladele, S., Oyedele, K.F., Dinyo, M.O. (2015): Pre-construction geoelectrical and geotechnical assessment of an engineering site at Alapere/Agboyi, Lagos, Nigeria. Ife Journal of Science, 17(3), pp. 543–552. OladeleS. OyedeleK.F. DinyoM.O. 2015 Pre-construction geoelectrical and geotechnical assessment of an engineering site at Alapere/Agboyi, Lagos, Nigeria Ife Journal of Science 17 3 543 552 Search in Google Scholar

Falae, P.O. (2014): Application of electrical resistivity in buildings foundation investigation in Ibese Southwestern Nigeria. Asia Pacific Journal of Energy and Environment, 1(2), pp. 95–107, DOI:10.15590/apjee/2014/v1i2/53748. FalaeP.O. 2014 Application of electrical resistivity in buildings foundation investigation in Ibese Southwestern Nigeria Asia Pacific Journal of Energy and Environment 1 2 95 107 10.15590/apjee/2014/v1i2/53748 Open DOISearch in Google Scholar

Soupois, P.M., Georgakopoulos, P., Papadopoulos, N., Saltos, V., Andreadakis, A., Vallianatos, F., Sanis, A., Markris, J.P. (2007): Use of engineering geophysics to investigate a site for a building foundation. Journal of Geophysics and Engineering, 4(1), pp. 94–103, DOI:10.1088/1742-2132/4/1/011. SoupoisP.M. GeorgakopoulosP. PapadopoulosN. SaltosV. AndreadakisA. VallianatosF. SanisA. MarkrisJ.P. 2007 Use of engineering geophysics to investigate a site for a building foundation Journal of Geophysics and Engineering 4 1 94 103 10.1088/1742-2132/4/1/011 Open DOISearch in Google Scholar

Farinde, M.A., Oni, S.O. (2015): Geophysical and geotechnical characterization of newly constructed Abadina-Ajibode road, University of Ibadan, Ibadan. Journal of Multidisciplinary Engineering Science and Technology (JMEST), 2(1), pp. 363–378. FarindeM.A. OniS.O. 2015 Geophysical and geotechnical characterization of newly constructed Abadina-Ajibode road, University of Ibadan, Ibadan Journal of Multidisciplinary Engineering Science and Technology (JMEST) 2 1 363 378 Search in Google Scholar

Alabi, A.A., Adewale, A.O., Coker, J.O., Ogunkoya, O.A. (2017): Site characterization for construction purposes at FUNAAB using geophysical and geotechnical methods. RMZ–Materials and Geoenvironment, 64, pp. 1–14, DOI:10.2478/rmzmag-2018-0007. AlabiA.A. AdewaleA.O. CokerJ.O. OgunkoyaO.A. 2017 Site characterization for construction purposes at FUNAAB using geophysical and geotechnical methods RMZ–Materials and Geoenvironment 64 1 14 10.2478/rmzmag-2018-0007 Open DOISearch in Google Scholar

Adejumo, S.A., Oyerinde, A.O., Aleem, M.O. (2015): Integrated geophysical and geotechnical subsoil evaluation for pre-foundation study of proposed site of vocational skill and entrepreneurship center at The Polytechnic, Ibadan, SW, Nigeria. International Journal of Scientific and Engineering Research, 6(6), pp. 2229–5518. AdejumoS.A. OyerindeA.O. AleemM.O. 2015 Integrated geophysical and geotechnical subsoil evaluation for pre-foundation study of proposed site of vocational skill and entrepreneurship center at The Polytechnic, Ibadan, SW, Nigeria International Journal of Scientific and Engineering Research 6 6 2229 5518 Search in Google Scholar

Akinse, A.G., Gbadebo, A.M. (2016): Geologic mapping of Abeokuta metropolis, southwestern Nigeria. International Journal of Scientific and Engineering Research, 7(8), pp. 2229–2518. AkinseA.G. GbadeboA.M. 2016 Geologic mapping of Abeokuta metropolis, southwestern Nigeria International Journal of Scientific and Engineering Research 7 8 2229 2518 Search in Google Scholar

Loke, M.H. (1999): Electrical imaging surveys for environmental and engineering studies; a practical guide to 2-D and 3-D surveys. Self-Published Note Book, pp. 15–57. LokeM.H. 1999 Electrical imaging surveys for environmental and engineering studies; a practical guide to 2-D and 3-D surveys Self-Published Note Book 15 57 Search in Google Scholar

Black, C.A. (1965): Methods of Soil Analysis. Part 1, American Society of Agronomy, No 9. BlackC.A. 1965 Methods of Soil Analysis Part 1, American Society of Agronomy No 9. Search in Google Scholar

Roy, T.K., Chattapadhyay, B.C., Roy, S.K. (2010): California bearing ratio evaluation and estimation: a study of comparison. Indian Geotechnical Conference, IGC-2010, IIT, Mumbai, pp. 19–22. RoyT.K. ChattapadhyayB.C. RoyS.K. 2010 California bearing ratio evaluation and estimation: a study of comparison Indian Geotechnical Conference, IGC-2010, IIT, Mumbai 19 22 Search in Google Scholar

Mookiah, M., Thiagarajan, S., Madhavi, G. (2015): Surface geo-electrical Sounding for the determination of aquifer characteristics in part of the Palar Sub-Basin, Tamilnadu, India. International Conference on Science Technology Engineering and Management [ICON-STEM’15], 8. MookiahM. ThiagarajanS. MadhaviG. 2015 Surface geo-electrical Sounding for the determination of aquifer characteristics in part of the Palar Sub-Basin, Tamilnadu, India International Conference on Science Technology Engineering and Management [ICON-STEM’15] 8 Search in Google Scholar

Federal Ministry of Works and Housing (FMW&H). (1997): General specification for roads and bridges. Vol II, Federal Highway Department, FMWH, Lagos, Nigeria, 168 p. Federal Ministry of Works and Housing (FMW&H) 1997 General specification for roads and bridges Vol II, Federal Highway Department, FMWH Lagos, Nigeria 168 Search in Google Scholar

Gidigasu, M.D. (1976): Laterite soil engineering (Pedogenesis and Engineering Principles). Elsevier Scientific Publishing Company: Amsterdam, 554 p. GidigasuM.D. 1976 Laterite soil engineering (Pedogenesis and Engineering Principles) Elsevier Scientific Publishing Company Amsterdam 554 Search in Google Scholar

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